Added `std.meta.staticIsSorted` to check if an `AliasSeq` is sorted according to some template predicate.

`std.meta.staticIsSorted` checks whether an `AliasSeq` is
sorted according to some template predicate.
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enum Comp(T1, T2) = T1.sizeof < T2.sizeof;

import std.meta : staticIsSorted;
static assert( staticIsSorted!(Comp, byte, uint, double));
static assert(!staticIsSorted!(Comp, bool, long, dchar));
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Additionally, the compile-time performance of `std.meta.staticSort` has been
greatly improved. Nevertheless, due to compiler limitations it is still an
extraordinarily expensive operation to perform on longer sequences; strive to
minimize such use.